1. Field of the Invention
Embodiments of the present invention relate to an organic insulator composition comprising a high dielectric constant insulator dispersed in a hyperbranched polymer, and an organic thin film transistor using the insulator composition. More particularly, embodiments of the present invention relate to an organic thin film transistor comprising a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode and an organic semiconductor layer wherein the gate insulating layer is made of an organic insulator composition comprising a high dielectric constant insulator dispersed in a hyperbranched polymer.
2. Description of the Related Art
General organic thin film transistors (OTFTs) comprise a substrate, a gate electrode, a gate insulating layer, source/drain electrodes, and a channel layer. Organic thin film transistors can be classified into bottom-contact (BC) OTFTs wherein an organic semiconductor layer is formed on source and drain electrodes, and top-contact (TC) OTFTs wherein metal electrodes are formed on an organic semiconductor layer by mask deposition.
Inorganic semiconductor materials, such as silicon (Si), have been commonly used as materials for organic semiconductor layers of OTFTs. However, with increasing demand for the manufacture of large-area, flexible displays at reduced costs, organic semiconductor materials are currently used as materials for organic semiconductor layers rather than inorganic semiconductor materials involving high costs and requiring high-temperature vacuum processes.
Organic thin film transistors are expected to be useful for driving devices of active displays and plastic chips for use in smart cards and inventory tags. The performance of such organic thin film transistors is evaluated in terms of their charge carrier mobility, threshold voltage, driving voltage and the like, and is comparable to that of α-Si TFTs.
Use of high dielectric constant insulators as materials for gate insulating layers is required to fabricate organic thin film transistors having superior electrical properties, including high charge carrier mobility. In this connection, U.S. Pat. Nos. 6,344,660 and 6,344,662 disclose thin film transistors using high dielectric constant insulators as materials for gate insulating layers. However, since the prior art devices are mainly dependent on vacuum processes for the formation of thin films, the fabrication of the devices incurs considerable costs.
U.S. Pat. No. 6,586,791 discloses an organic thin film transistor using a gate insulating layer made of nanometer-scale ceramic particles (200 nm or below) dispersed in a polymer matrix. At this time, a linear polymer, e.g., epoxy, polyimide or polyetherimide, is used as the polymer matrix for dispersing the ceramic particles. However, since the linear polymer has a relatively high viscosity in relation to its molecular weight, it has a problem of non-uniform coating.